https://www.amazon.com/Fender-Jbass-Orig-Thumbrest-Black/dp/B0002E2G5Q/ref=sr_1_2?keywords=bass+thumb+rest&qid=1678674001&sr=8-2

https://www.amazon.com/Artibetter-Rosewood-Guitar-Finger-Mounting/dp/B07VNCC68R/ref=sr_1_4?keywords=bass+thumb+rest&qid=1678674001&sr=8-4

I don't think these are usually intended to sit above the strings, but I think they'd do just fine.